From: Mark Kettenis Subject: Re: spread 8 network interrupt over cpu and softnet To: Alexander Bluhm Cc: tech@openbsd.org Date: Fri, 03 Oct 2025 16:27:33 +0200 > Date: Sat, 27 Sep 2025 18:36:50 +0200 > From: Alexander Bluhm > > Hi, > > Currently most network drivers use 8 queues and distribute interrupts. > ix(4) is the only one that may allocate more than 8. ice(8) uses > only 8 vectors, but allocates more interrupts. > > I would like to limit interrupts and queues to 8 for all drivers. > This prevents running out of interrupt vectors so easily. Here's a nickel boy; go buy yourself a better computer! Joking aside, we shouldn't waste resources and I it is plausible that using the maximum number of queues provided by the hardware isn' optimal. > Currently we have 8 softnet threads which limits parallel processing > anyway. We can tune these values later. Does it even make sense to have more rx queues than softnet threads? Should there be a single limit for both? > With this diff, forwarding througput increases from 45 to 50 GBit/sec > on my 12 core machine from ice0 to ice1. I am using iperf3 TCP on > Linux to measure it. I think slower performance happend because > ice(4) was allocating more interrupts than it has vectors. Now > everything is limited to 8. For other drivers I see no difference > as they operate at line speed anyway. > > I think arbitrary numbers IXL_MAX_VECTORS, IGC_MAX_VECTORS and > IGC_MAX_VECTORS could go away, but that would be per driver diffs. > > Second part of the diff spreads the interrupts of network devices > equally over the softnet tasks. That is this line: > - ifq->ifq_softnet = net_tq(idx); > + ifq->ifq_softnet = net_tq(ifp->if_index * IF_MAX_VECTORS + idx); Does this even do anything given that both IF_MAX_VECTOR and the number of softneq threads is 8? Doesn't this simply reduce to: (ifp->if_index * 8 + idx) % 8 = idx Maybe it is better to stagger the interrupts instead? Like ifq->ifq_softnet = net_tq(ifp->if_index + idx); ? > Index: dev/pci/if_bnxt.c > =================================================================== > RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_bnxt.c,v > diff -u -p -r1.56 if_bnxt.c > --- dev/pci/if_bnxt.c 5 Sep 2025 09:58:24 -0000 1.56 > +++ dev/pci/if_bnxt.c 25 Sep 2025 08:27:45 -0000 > @@ -545,9 +545,11 @@ bnxt_attach(struct device *parent, struc > nmsix = pci_intr_msix_count(pa); > if (nmsix > 1) { > sc->sc_ih = pci_intr_establish(sc->sc_pc, ih, > - IPL_NET | IPL_MPSAFE, bnxt_admin_intr, sc, DEVNAME(sc)); > - sc->sc_intrmap = intrmap_create(&sc->sc_dev, > - nmsix - 1, BNXT_MAX_QUEUES, INTRMAP_POWEROF2); > + IPL_NET | IPL_MPSAFE, bnxt_admin_intr, sc, > + DEVNAME(sc)); > + sc->sc_intrmap = intrmap_create(&sc->sc_dev, nmsix - 1, > + MIN(BNXT_MAX_QUEUES, IF_MAX_VECTORS), > + INTRMAP_POWEROF2); > sc->sc_nqueues = intrmap_count(sc->sc_intrmap); > KASSERT(sc->sc_nqueues > 0); > KASSERT(powerof2(sc->sc_nqueues)); > Index: dev/pci/if_ice.c > =================================================================== > RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_ice.c,v > diff -u -p -r1.59 if_ice.c > --- dev/pci/if_ice.c 17 Sep 2025 12:54:19 -0000 1.59 > +++ dev/pci/if_ice.c 27 Sep 2025 07:35:25 -0000 > @@ -30501,7 +30501,8 @@ ice_attach_hook(struct device *self) > sc->sc_nmsix = nmsix; > nqueues_max = MIN(sc->isc_nrxqsets_max, sc->isc_ntxqsets_max); > sc->sc_intrmap = intrmap_create(&sc->sc_dev, sc->sc_nmsix - 1, > - nqueues_max, INTRMAP_POWEROF2); > + MIN(MIN(nqueues_max, ICE_MAX_VECTORS), IF_MAX_VECTORS), > + INTRMAP_POWEROF2); > nqueues = intrmap_count(sc->sc_intrmap); > KASSERT(nqueues > 0); > KASSERT(powerof2(nqueues)); > Index: dev/pci/if_igc.c > =================================================================== > RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_igc.c,v > diff -u -p -r1.28 if_igc.c > --- dev/pci/if_igc.c 24 Jun 2025 11:00:27 -0000 1.28 > +++ dev/pci/if_igc.c 27 Sep 2025 07:29:57 -0000 > @@ -724,8 +724,8 @@ igc_setup_msix(struct igc_softc *sc) > /* Give one vector to events. */ > nmsix--; > > - sc->sc_intrmap = intrmap_create(&sc->sc_dev, nmsix, IGC_MAX_VECTORS, > - INTRMAP_POWEROF2); > + sc->sc_intrmap = intrmap_create(&sc->sc_dev, nmsix, > + MIN(IGC_MAX_VECTORS, IF_MAX_VECTORS), INTRMAP_POWEROF2); > sc->sc_nqueues = intrmap_count(sc->sc_intrmap); > } > > Index: dev/pci/if_ix.c > =================================================================== > RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_ix.c,v > diff -u -p -r1.221 if_ix.c > --- dev/pci/if_ix.c 24 Jun 2025 11:02:03 -0000 1.221 > +++ dev/pci/if_ix.c 25 Sep 2025 08:27:45 -0000 > @@ -1854,7 +1854,8 @@ ixgbe_setup_msix(struct ix_softc *sc) > /* XXX the number of queues is limited to what we can keep stats on */ > maxq = (sc->hw.mac.type == ixgbe_mac_82598EB) ? 8 : 16; > > - sc->sc_intrmap = intrmap_create(&sc->dev, nmsix, maxq, 0); > + sc->sc_intrmap = intrmap_create(&sc->dev, nmsix, > + MIN(maxq, IF_MAX_VECTORS), 0); > sc->num_queues = intrmap_count(sc->sc_intrmap); > } > > Index: dev/pci/if_ixl.c > =================================================================== > RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_ixl.c,v > diff -u -p -r1.109 if_ixl.c > --- dev/pci/if_ixl.c 17 Sep 2025 12:54:19 -0000 1.109 > +++ dev/pci/if_ixl.c 27 Sep 2025 07:29:57 -0000 > @@ -1782,8 +1782,9 @@ ixl_attach(struct device *parent, struct > if (nmsix > 1) { /* we used 1 (the 0th) for the adminq */ > nmsix--; > > - sc->sc_intrmap = intrmap_create(&sc->sc_dev, > - nmsix, IXL_MAX_VECTORS, INTRMAP_POWEROF2); > + sc->sc_intrmap = intrmap_create(&sc->sc_dev, nmsix, > + MIN(IXL_MAX_VECTORS, IF_MAX_VECTORS), > + INTRMAP_POWEROF2); > nqueues = intrmap_count(sc->sc_intrmap); > KASSERT(nqueues > 0); > KASSERT(powerof2(nqueues)); > Index: net/if.h > =================================================================== > RCS file: /data/mirror/openbsd/cvs/src/sys/net/if.h,v > diff -u -p -r1.221 if.h > --- net/if.h 9 Sep 2025 09:16:18 -0000 1.221 > +++ net/if.h 25 Sep 2025 08:27:45 -0000 > @@ -526,6 +526,9 @@ struct if_sffpage { > #include > > #ifdef _KERNEL > + > +#define IF_MAX_VECTORS 8 > + > struct socket; > struct ifnet; > struct ifq_ops; > Index: net/ifq.c > =================================================================== > RCS file: /data/mirror/openbsd/cvs/src/sys/net/ifq.c,v > diff -u -p -r1.62 ifq.c > --- net/ifq.c 28 Jul 2025 05:25:44 -0000 1.62 > +++ net/ifq.c 25 Sep 2025 08:27:45 -0000 > @@ -255,7 +255,7 @@ void > ifq_init(struct ifqueue *ifq, struct ifnet *ifp, unsigned int idx) > { > ifq->ifq_if = ifp; > - ifq->ifq_softnet = net_tq(idx); > + ifq->ifq_softnet = net_tq(ifp->if_index * IF_MAX_VECTORS + idx); > ifq->ifq_softc = NULL; > > mtx_init(&ifq->ifq_mtx, IPL_NET); > >